1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus for a copying machine, a printer, a facsimile, or a multifunction apparatus having functions of these devices, or the like.
2. Description of the Related Art
In general, in an electrographic method, an electrostatic recording method, or the like, an electrostatic latent image is formed on an image carrier, such as a photosensitive drum, and the electrostatic latent image is formed into a visible image with use of a toner serving as a developing agent. The thus-visualized toner image is subjected to a transfer process and a fixation process, whereby an image is formed on recording paper (a recording material, a recording medium, paper). In such an image forming method, residual toner (remaining toner) usually remains on an image carrier after a transfer process. Accordingly, a cleaning device for cleaning the residual toner is disposed.
Cleaning devices of various types have been known as such a cleaning device. Typical examples thereof include a cleaning device of blade-cleaning type, in which a cleaning blade made from a contact plate usually having elasticity is disposed so as to come into contact with an image carrier, to thus cause the cleaning blade to scrape residual toner from the image carrier. In this blade-cleaning method, since a cleaning blade comes into contact with a surface of an image carrier, such as a photosensitive drum, to thus be rub the same, an edge of the cleaning blade for scraping toner becomes worn.
In addition, in, e.g., a lower-speed or a medium-speed apparatus, an electrifying device of a contact type, such as a charging roll, is generally employed as an electrifying member. A reason why such an electrifying device is employed is that the electrifying device produces a drastically smaller amount of ozone as compared with an on-contact-type electrifying device, such as a so-called corotron charging device, thereby being friendly to the environment. Moreover, other reasons for employing the contact-type electrifying device include ready realization of miniaturization and cost reduction, since neither an ozone filter nor an air blower is necessary.
Meanwhile, there arises a problem that an amount of corona products adhering to a photosensitive drum is drastically increased as compared with a non-contact-type electrifying device. The cause thereof is that a contact-type electrifying device produces a smaller absolute amount of corona products than does a non-contact-type electrifying device, however, a discharge region of the former is in very close proximity to a photosensitive drum. Accordingly, when a cleaning blade is employed in a contact-type electrifying device, in addition to abrasion of the cleaning blade caused by an increase in frictional coefficient, problems of chipping and turning-up of the same arise, along with an increase in torque of a photosensitive-material-driving section.
Meanwhile, for the purpose of increasing abrasion resistance of a photosensitive drum, an image carrier whose outermost surface layer contains a charge-transport material and a siloxane resin, and which is of high mechanical strength, has hitherto been disclosed (see, e.g., JP-A-11-38656, JP-A-11-184106, or JP-A-11-316468). These image carriers having high mechanical strength exhibit a tendency such that corona products having been effectively removed by means of abrasion in a related-art image carrier are less-easily removed, thereby increasing friction to a large extent, to thus further exacerbate damage to a blade.
A variety of methods for suppressing abrasion, chipping, and turning-up of a cleaning blade and an increase in a torque or a photosensitive-material-driving section have hitherto been proposed.
There has been known a method of, for the purpose of maintaining lubricity between the surface of a photosensitive material and a cleaning blade, periodically producing a toner band on a region where no image is to be formed and supplying the same to a blade edge (see, e.g., JP-A-4-005679 (pages 2 to 3, FIG. 1) or JP-A-3-180884 (page 3, FIG. 2)). A method of supplying lubricant to the surface of a photosensitive material byway of a lubricant-application member has also been known (see, e.g., JP-A-2003-330318 (page 5, FIG. 3)).
In addition to the above, there has been known a method of, for the purpose of reducing a frictional force with respect to a cleaning blade, rubbing the surface of an image carrier with a magnetic brush or a sponge roll containing a polishing agent, thereby removing corona products from the surface of the image carrier (see, e.g., JP-A-10-143039 (page 4, FIG. 2) or JP-A-10-143039 (page 4, FIG. 2)).
However, according to JP-A-4-005679 or JP-A-3-180884, an amount of toner to be consumed will be increased by an amount for producing the toner band, which is required in addition to that for forming a desired image, which is unfavorable.
According to JP-A-2003-330318, JP-A-10-143039, or JP-A-10-143039, cost is increased for disposing lubricant-application means and corona-products-removal means, and a problem of space saving also arises.